B VITAMINS: WHAT THEY ARE 13 



biocatalysts of low molecular weight, regardless of their nutritional 

 significance or insignificance. 



The search for substances which are potentially B vitamins is an active 

 one at the present time. Advance in this field is so rapid that this mono- 

 graph cannot hope to carry up-to-the-minute information. It is not sur- 

 prising that the author of this section should be in possession of a certain 

 amount of unpublished information which is pertinent to this discussion. 

 The only safe procedure in view of the activity in this field, however, 

 seems to be to treat all unpublished information which may be in the 

 writer's possession as though it did not exist. The discussions which 

 follow will, therefore, be based almost entirely upon results which have 

 received general publication. 



If we retain the nutritional point of view with respect to the meaning 

 of the term "vitamin," then before any new substance can be accepted 

 as a member of the family, evidence must be available with respect to 

 its nutritional need by animals. We shall therefore discuss first those 

 substances for which such need has been demonstrated. 



Second, before any growth factor can be discussed intelligently, its 

 unitary nature and its existence as a chemical entity must be reasonably 

 well established. In order to meet this criterion, the substance in question 

 must have been characterized chemically or concentrated to a relatively 

 high degree. 



Before we inquire what is meant by "concentrating a vitamin to a 

 high degree," it will be well to look at some historical data with respect 

 to the vitamins which are already well recognized. 



Rice polish was the starting material used for the first isolation of 

 thiamine. It contains in round figures 33 /tg of thiamine per gram. 

 Thiamine is therefore about 30,000 times as active physiologically as rice 

 polish, and this figure represents the extent to which concentration had 

 to be carried to yield the active principle. Using the same type of calcu- 

 lation, we arrive at the values for the typical B vitamins listed below. 



From these data we may infer that before a new vitamin is obtained in 

 pure form, it is probable that it will have to be concentrated several 

 thousand times at least, starting with any rich natural source as a refer- 



